Method of making lignin compound and product



' bonding agent.

Patented Dec. 18, 1951 METHOD OF MAKING LIGNIN COMPOUND AND PRODUCTWorth C. Goss, Seattle, Wash, assignor to United States SheetwoodCompany, Seattle, Wash., a

corporation of Delaware No Drawing. Application June 26, 1948, SerialNo. 35,519

4 Claims.

This inventionrelates to the making of new and useful chemicalcompounds.

More particularly, the present invention has to do with the making ofnew chemical compounds, to be used principally as glues, binders and thelike, and possessing desirable characteristics and having certainadvantages of use over and beyond products heretofore applied to thoseuses for which the present compounds are to be applied; the presentcompounds being produced by reactions between certain selectedsubstances of which a chemically depleted form of lignin is one of primeimportance.

It is the principal object of my invention to produce new resincompounds that have the following desirable characteristics; They arewell adapted for useas glues or bonding agents; they are thermo-settingbut only at a relatively high degree of heat, for example, attemperatures over 225 F.; they can be easily and inexpensivelymanufactured; they are easy to use and are especially suitable for useas a bonding and waterproofin agent in the manufacture of sheet woodproducts, and the like, whereinthe present compounds are mixed with woodfibers and the mixture compressed and set under the action of heat andmechanically applied pressure.

To impart a better understanding of some of the objects which I desireto attain by and the advantages residing in the present invention, itwill here be explained that in a copending application, Serial No.3,000, filed January 19, 1948, I have described the making of boards, orsheet Wood products, from moist, fiberized, ligno-cellulosic materialsand a thermo-setting, plastic More specifically, I have described themaking of sheet wood from a mixture of moist wood fibers and a specialbonding agent derived by the wet grinding of wood that has decayed to acondition of brown rot; the mixing of materials as described beingaccomplished by passing the damp wood fibers and the bonding agent,which is of paste-like consistency, together through a mixing machinethat operates in such manner as to cause the coatin of the individualfibers with the agent. The coated fibers were then sifted through aseries of screens and allowed to fall from suspension in air, to form apad, the pad then being consolidated in a hot platen press and thefibers thereof coalesced together and the agent set under the action ofheat and pressure thus applied.

In my manufacture of sheet wood products according to the abovedescription, I have found it necessary, for the most efiective and quickcoalescing and bonding of the fibers, that the mixture should contain acertain amount of moisture to be generated into steam under the heat ofthe press. However, it is advantageous to fast and economicalmanufacture, that the moisture content be kept at as low a percentage aspracticable without detriment to the finished product.

Where wood fibers, preparatory to the consolidating operation, areformed or felted into sheets by any of the commonly used wet lapprocesses, the moisture content of the sheet will be extremely high.Because of this, it has been the general practice to pass these sheetsas formed by the wet lap process, through squeeze rolls to expel acertain amount of the excess moisture therefrom before the sheet isdelivered into the consolidating press. In spite of this squeeze rollpre-pressing operation, the moisture content of the sheets will stillremain quite high and by reason of this high moisture content, thepressing time, or drying time required in the press will be prolongedaccordingly.

In accordance with the teachings of the previously mentioned copendingapplication, the bondin agent of thin, paste-like consistency,containing a substantial amount of moisture as derived by the wetgrinding of brown rotted wood, is mixed with the damp wood fibers insuch amount that although each fiber is given a thin coating of theagent, the agent, which is not tacky, is not applied in amountsufficient to cause the adherence of fibers or the balling of themixture in the mixing operation, or as discharged from the mixer. Infact, the coated fibers may be readily separated by a shaker screenoperation to fall from suspension in air for the formation of padstherefrom. However, the mixture, as prepared, still containsapproximately of moisture, which is an amount advantageous to the methodof mixin which I employ, but considerably more than is required for theproduction of that amount of steam necessary to insure proper coaelscingof fibers under the effects of heat and pressure as produced by thepress. Therefore, I have found it to be quite advantageous for fasterpressing operations, to fur- .ther reduce the moisture content of themixture to approximately 25% by passing it through a suitable dryerbefore forming it into pads for consolidation.

Heretofore, there has been an objection or disadvantage to this furtherdrying out of the coated fibers, by heat, the objection arising from thefact that under a normal drying heat of around 200 F. to 225 F., thebonding agent, prepared as described in my prior application and appliedto the fibers in the form of a thin coating, is subject to pre-settingto more or less amount and thus the finished boards do not have fullshear 3 strength. Therefore, the drying of the coated fibers, prior toforming them into pads for consolidation, has not been made a practice.Thus, a faster pressing time with incident decrease of cost has beensacrificed in the interest of additional strength in the finishedproduct.

In view of the foregoing explanation, it has been an object of thisinvention to produce a series of chemical compounds, designed to replacethe bonding agents previously used, which are not only especiallyeffective glues or bonding agents, giving more toughness to the productsand increasing shear strength considerably, but also, and most importantto the present use, are characterized by the fact that the tendency topre-set is substantially reduced at the temperatures coming within therange that is desired for the dryin out of excessive moisture from thecoated fibers preparatory to forming them into sheets or pads forcompression.

The present compounds may be produced by compounding various chemicalswith what I have designated as a chemically depleted lignin such as thatsubstance comprising the major portion of wood that has decayed to acondition of brown rot. I find it quite practical to carry out theinvention, in one way, by reacting together brown rotted wood, ammoniumhydroxide, and a selected phenol; for example, I may use resorcinol,pyrocatechol, carbolic acid, cresylic acid or cresol. Some othercompounds that may be used are furfural, furfural alcohol, urea, maleicanhydride, petroleum distillation products higher and lower boiling thancresylic acid, various aldehydes and the higher alcohols such asglycerine.

The term brown rotted wood as herein used, which is one source ofchemically depleted lignin, is intended to be descriptive of forest woodthat either has decayed to a condition of brown rot by natural process,or has been artificially reduced to that condition by subjecting thewood to the action of certain micro-organisms, such as, for example,those known as polyporous Schweinitzii. Wood that has decayed to thecondition of brown rot, either by natural process or by artificiallyproduced conditions, is not to be confused in this instance with otherforms of rot, for example the white rot sometimes found in forest wood.Furthermore, brown rotted wood is here understood to be a material whichanalyzes about 70% or more of lignin by acid analysis; the cellulose ofthe wood having been removed from the material by the celluloseconsuming micro-organisms or fungi. This brown rotted wood is one sourceof what I have designated as a chemically depleted form of lignin, andby reason of its chemical depletion, this form of lignin has an extremedegree of chemical activity as compared with that of ordinary lignin,such as pulp liquor lignin.

To better explain what I mean by my use of the term chemical depletion,or chemically depleted, it will here be pointed out that lignin fromfresh Douglas fir wood analyzes 15.4% methoxyl content, while the ligninextracted from brown rotted Douglas fir wood analyzes only 11.6%methoxyl content. There also is a gradation in chemical depletion in thebrown rotted material as indicated by a further analysis which wascarried out as follows: Brown rotted wood was added to a solution ofammonium hydroxide at a temperature of 170 F. About 20% of the brownrotted wood was dissolved, forming a very dark colored solution. Thesolution was separated from the solid portion by filtration, and

the filtrate was acidified with hydro-chloric acid and a brownprecipitate appeared. This precipitate, on acid analysis, showed 88%lignin content, and this lignin showed a methoxyl content of only 7.9%.

My definition of depleted lignin as used in the present instance, andregardless of its source, is: A. substance essentially lignin incharacter but containing less methoxyl content than the lignin of thevegetable substance from which the depleted lignin comes. Black forestsoil has a depleted lignin of even lower methoxyl content than that ofbrown rotted wood, and this is also true of peat. In general, thedepleted lignins are acidic in character, and my experiments have shownthat the lignin that is most depleted, that is, which has the lowestmethoxyl content, has the most vigorous chemical reaction with ammoniumhydroxide and any selected phenol or substance used in lieu of a phenol.

Sources of depleted lignin suitable for use in carrying out the presentinvention are black forest soil, peat, lignite coal, animal manure,artificially produced depleted lignin, and the brown rotted woodpreviously defined.

A satisfactory method of forming the present product, or chemicalcompound, is as follows:

Brown rotted wood, in accordance with the previous definition of thismaterial, is wet ground to a very fine, paste-like consistency. Grindmaybe very satisfactorily accomplished by use of a Carborundum plateattrition mill. One pound of dry brown rotted wood and five pounds ofwater can be ground in such a mill to form a paste of very satisfactoryconsistency for the present uses in the manufacture of pressed wood orsheet wood from wood fibers. The proportions used may be varied to someextent from those above given without detriment to the final product.

To the rotted wood paste thus formed, I then add ammonium hydroxide,while stirring the mixture, until it shows a pH of about 9.2.

Explanatory to the addition of the ammonium hydroxide, it will be herenoted that in my previously referred to application, I disclosed thewashing of the brown rotted wood with a solution of ammonium. hydroxidein order to neutralize the humic acids contained therein which weredetrimental to fiber strength in the finished products. In the presentinstance, where the base material is a depleted lignin to be obtainedfrom various sources which are, in general,

acidic in character, it is desirable to add the ammonium hydroxide notonly because of its neutralizing effect on the acidic content, butprimarily in order to bring about the reaction between the varioussubstances used in forming the compounds, for without it, or itsequivalent, the proper compounds are not prepared nor are the objects ofthe invention attained.

After the ammonium hydroxide has been added to the rotted wood paste tothe extent above specified, I then add to the mixture twotenths of apound of a selected phenol, for example, resorcinol, for each pound ofdry rotted wood used in making the mixture. The mixture is then stirredthoroughly and is thereby made ready for use.

In the manufacture of this compound, I have also used phenols other thanresorcinol with satisfactory results. For example, in lieu ofresorcinol, I can use any of those previously named with more or lesssuccess. Should the 5; compound be made by use of another phenol. in

lieu of resorcinol, the selected phenol would be used in a like mannerand in an amount equivalent to that given above for resorcinol, and whenso used, a similar resin compound will result therefrom.

An excellent resin compound may also be produced by the three-wayreaction between brown rotted wood, ammonium hydroxide and urea in lieuof a phenol.

Another good resin compound is prepared using furfural in place of urea.

An example of preparing the product by the use of urea is as follows:

For each ten parts by weight or" dry brown rotted wood, I add two partsby weight of urea and sixty parts by weight of water. This mixture isthen ground to a smooth, soup-like consistency which will have a pH ofabout 3.3. Ammonium hydroxide is then added slowly thereto whilestirring the mixture, until the pH of the mixture reaches 9.0 or over.The new chemical compound thus produced may be used directly as a heatsetting glue. of this glue by weight (dry basis) mixed as previouslydisclosed with 85% wood fibers, and the mixture dried to a moisturecontent of from 15 to 75%, may be pressed under a temperature of 250 F.and above to form a strong, hard, split-proof board especially suitablefor receiving thin plastic overlay sheets.

Mixing of materials in the instance of use of urea also would preferablybe in accordance with the teaching of my copending applicationpreviously mentioned. The ammonium hydroxide soluble portion of thebrown rotted wood proves to make the best resin. This soluble portionshows a lignin content of 88%, which lignin has a methoxyl content offrom 7 to 10%.

It is not the intent that the compounding of the present glue or binderbe restricted to use of ammonium hydroxide as the agent for neutralizingthe acid content of the brown rotted wood and promoting the reactionbetween the various substances used. In lieu of ammonium hydroxide,other basis nitrogen compounds such as the amines, or quaternary ammoniabases, might be used with a substantial degree of success.

In the preparation of a product using black forest soil as the source ofdepleted lignin, I proceed as follows: A quantity of black forest soilis put in a vat together with strong ammonium hydroxide. This is heatedat a temperature of about 170 F. for a period of about one hour. I thendrain the contents of the vat into a centrifuge and by that meansseparate the black liquor resulting from the treatment of soil from thesludge. This black liquor, which contains the depleted lignin therein,is concentrated by evaporation and may then be used as the basicmaterial of the present product. The compound is then completed by theaddition of a phenol thereto as previously described, or by the additionof urea, or other suitable substance.

To extract depleted lignin from lignite coal, I proceed as follows: Thecoal is first ground to a fine powder. This powder is boiled in a 1%solution of sodium hydroxide for a period of thirty minutes. The blackliquor is then centrifuged from the sludge and the black liquorneutralized with hydrochloric acid, and this results in a dark coloredprecipitate being formed. The precipitate is separated by centrifugingor filtering and is washed with clear water. This precipitate isconstituted principally of depleted lignin and is a very excellentstarting material for my new compound. It is used with ammoniumhydroxide and urea or ammonium hydroxide and a phenol, as has previouslybeen described.

The present compounds as produced by the reaction between depletedlignin, from any of the mentioned sources, ammonium hydroxide and aphenol, or urea, or other substances, is characterized by the propertyof giving exceptional toughmess to wood fiber products wherein thecompounds are used as bonding agents. It very automatically increasesshear strength and increases water'resistance. The same characteristicswill be found in products regardless of the source of depleted ligninused therein. However, because of its great abundance, the ease of useand excellency of the product produced therefrom, brown rotted Wood isnow the preferred source of depleted lignin.

Having thus described my invention, what I claim as new therein anddesire to secure by Letters Patent is:

1. The method of making a high temperature, thermo-setting compoundcomprising wet grinding brown rotted Wood to a paste, adding theretoammonium hydroxide until the mixture shows a pH of about 9.2, thenreacting the neutralized substance with a phenol selected from the groupconsisting of resorcinol, pyrocatechol, carbolic acid, cresylic acid,and cresol.

2. The method of making a high temperature, thermo-setting resincomprising wet grinding brown rotted wood to a paste, mixing ammoniumhydroxide therewith until the mixture shows a pH of about 9.2, thenadding approximately oneiifth pound, for each pound of dry brown rottedwood used in the mixture, of a phenol selected from the group consistingof resorcinol, pyrocatechol, carbolic acid, cresylic acid and cresol.

3. The method of making a high temperature, thermo-setting resincomprising mixing a brown rotted wood with ammonium hydroxide until themixture shows a pH of about 9.2, then reacting, with the mixture, of aphenol selected from the group consisting of resorcinol, pyrocatechol,carbolic acid, cresylic acid and cresol.

4. A high temperature, thermo-setting binder comprising a mixture ofbrown rotted wood,

1 ammonium hydroxide and a phenol selected from the group consisting ofresorcinol, pyrocatechol, carbolic acid, cresylic acid and cresol.

WORTH C. GOSS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Rose et al.: Journal Ind. Eng.Chem, March 1917, pages 284-287.

Thaysen et al.: The Microbiology of Cellulose, 1927, page 300.

4. A HIGH TEMPERATURE, THERMO-SETTING BINDER COMPRISING A MIXTURE OFBROWN ROTTED WOOD, AMMINIUM HYDROXIDE AND A PHENOL SELECTED FROMCARBOLIC ACID, CRESYLIC ACID AND CRESOL.